The invention relates to a plasma display panel comprising a first, transparent substrate provided with at least two display electrodes, a second substrate provided with a fluorescent material, in which, at least during use, display electrodes and address electrodes define pixels, and comprising a gas discharge mixture between the two substrates.
The address electrodes may be present on both the first and the second substrate. The fluorescent material is patterned or not patterned, dependent on the type of display device.
A display panel of this type is used, inter alia, in large, flat display screens, for example, for HDTV.
A plasma display panel (PDP) of the type described above is known from EP-A-0 779 643. This document states measures of raising the luminance of such a panel. Inter alia, a favorable composition of the gas discharge mixture (between 10% and less than 100% xenon) is proposed for this purpose. A higher percentage of xenon is assumed to increase the quantity of UV radiation and thus to increase the number of photons incident on the fluorescent material for converting UV radiation into visible light.
A plasma display panel according to the invention is characterized in that the layer of fluorescent material comprises at least one non-saturating green phosphor.
A non-saturating phosphor is herein understood to mean a phosphor in which the number of emitted photons per unit of time and area at a drive (voltage) leading to a luminance of 500 Cd/m2 decreases at most 15% with respect to a drive (voltage) leading to a luminance of 10 Cd/m2. Using excitation by means of a UV-plasma, maintained with AC voltage, this means for example that the efficacy (number of emitted photons/number of incoming photons) decreases by at most 15% at higher frequencies (at least up to 30 kHz and preferably up to 100 kHz or more).
The invention is based on the recognition that, notably at the frequencies at which plasma display panels are operated in the xe2x80x9csustain modexe2x80x9d (sustain frequency (in practice 30-300 kHz)) the total efficacy is much more dependent on the capacity of the phosphors used to convert UV radiation into visible light than on the effectiveness of increasing the quantity of UV radiation. A frequently used green phosphor such as Zn2SiO4:Mn (willemite) has saturation phenomena from already approximately 1 kHz. The efficacy (number of emitted photons/number of incoming photons) has already decreased to approximately 90% and rapidly decreases at higher frequencies (down to approximately 50% at 100 kHz).
On the other hand, the efficacy remains substantially constant throughout a large frequency range when non-saturating phosphors are used.
A suitable non-saturating green phosphor is, for example (Ce,Gd)MgB5O10:Tb, or CBT.
A preferred embodiment of a plasma display panel according to the invention is characterized in that the display panel comprises drive means for sustaining a generated plasma with a pulse pattern (sustain voltage) whose peak-to-peak voltage is at least 400 V.
This can be combined with existing red and blue phosphor to obtain the right color.
Since non-saturating phosphors are used, the increase of this voltage leads to a higher light output. When saturating phosphors are used, such an increase of this voltage has hardly any effect. It is true that the amount of generated UV radiation in the plasma is increased by a raised voltage, but the efficacy of converting UV radiation into visible light decreases at higher frequencies for saturating phosphors.